The present invention is an apparatus and method for ultra wide band (UWB) radar holographic detection and imaging. The present invention relates generally to the field of ground penetrating radar (GPR) with a unique illumination method for detecting and imaging non-uniform objects.
Previously, it has been shown that metallic and non-metallic type objects concealed within or close to the surface of the earth can be detected by conventional metal detectors, and with conventional GPR radar searching apparatuses. The most widely practiced technology for detection of near surface metallic objects has been the conventional xe2x80x9cmetal detectorxe2x80x9d device.
The first major obstacle in fielding a reliable GPR radar system arises when attempting to detect foreign objects in a relatively uniform mass having a similar electromagnetic impedance (dielectric constant) as the foreign object. When a buried object has a similar dielectric constant to the surrounding soil, it is essentially hidden from a conventional GPR searching radar signal. For example, plastic mines are constructed with materials that are typically the same electromagnetic impedance (dielectric constant) as dry sand produce extremely small reflections back to the searching radar. The typical dielectric constant for dry sand is from 3 to 4. GPR experiments with simulated plastic mines (inert explosive) supplied by the U.S. Army (Fort Belvoir) indicate these small reflections are less than 0.5 db above the sand reflection. If the radar is to detect these small mines, the surface reflection and the mine""s reflection must be separated.
A typical metal detector is essentially ineffective and useless in the detection of small non-uniform objects buried in a relative uniform mass having a similar electromagnetic impedance as the foreign object. Current GPR systems use low frequencies (xcx9c250 MHz to 1 GHz) and vertical illumination techniques and are ineffective in detecting and imaging small near surface plastic mines because (1) the low frequency GPR wave lengths are to long for accurately imaging the small mines and (2) the mine""s small reflections are concealed in the strong surface reflection which is not deflected away from the receiver.
The second major obstacle for conventional GPR is the lower frequencies limit the imaging (object characterization) capability of the systems since resolution is proportional to wavelength (inversely proportional to frequency). The lower frequency in such systems inhibit their ability to generate high enough resolution xe2x80x9c3-Dxe2x80x9d images in order to identify small objects such as anti-personnel (AP) mines even if they were able to detect them. To effectively image (accurately size) and characterize objects the radar wavelength must be smaller than the object. Typically, AP plastic mines are approximately 2 cm in diameter and conventional GPR radar wavelengths (xcx9c70 cm to 20 cm) are much greater than these dimensions. This relationship negates imaging them with any degree of resolution for identification purposes.
The present invention is an apparatus for displaying a foreign body in a relatively uniform mass having similar electromagnetic impedance as the foreign body comprising of at least two ultra wide band holographic radar units adapated to generate, transmit and receive a plurality of 12-20 GHz frequency signals in a dual linear antenna with slant-angle illumination. The radar units have at least one transmitting antenna adapted to transmit the 8-20 GHz frequency signals generated from the radar unit wherein the transmitting antenna defines an acute angle relative to the surface of the relatively uniform mass. Moreover, the radar units have at least one receiving antenna adapted to receive a plurality of reflected signals from the foreign body wherein the receiving antenna defines an acute angle relative to the surface of the relatively uniform mass.
The present invention further comprises of a radar unit having at least one holographic transceiver adapted to process the received signal wherein the transceiver comprises of a high voltage controlled oscillator and at least one lower frequency oscillator.
The radar units further having at least one first signal transporter for transporting the received signals from the receiving antenna and to the transceiver. The radar units further having at least one second signal transporter for transporting the processed signal from transceiver and to a imaging display unit. The radar units further having at least one imaging display unit adapted to display a plurality of the process signals.
A further aspect of the present invention determines the presence of the foreign body by identifying the presence of signal intensity peaks in the reflected signal. The depth of the foreign body is indicated by the difference in time of the appearance of the signal intensity peaks.
A typical embodiment of the present invention places the transmitting and receiving antennas at an acute angle of about 20 degrees to about 40 degrees with respect to the surface of the relatively uniform mass. A more preferred embodiment of the present invention places the transmitting and receiving antennas at an acute angle of about 30 degrees with respect to the surface of the relatively uniform mass.
A further aspect of the present invention is a method of detecting and imagining foreign objects in a relative uniform mass comprising the steps of generating a plurality of 12-20 GHz frequency wide band signals from at least two holographic radar units wherein said holographic radar unit comprises of at least one transmitting antenna and at least one receiving antenna: A typical method is transmitting at least one 12-20 GHz frequency wide band signal at a first acute angle relative to the surface of a relatively uniform mass, and receiving at least one reflected signal at a second acute angle relative to the surface of said relatively uniform mass. The received signal is transmitted by a first signal transporter from receiving antenna and to a holographic transceiver. The transported signal is processed with at least one holographic transceiver. A processed signal is transported by a second signal transporter from at least one transceiver and to at least one imaging display unit, where the processed signal is displayed.
Another aspect of this present invention is a method wherein a transmitting and receiving antennae are positioned typically at an acute angle of between about 20 degrees and up to about 40 degrees with respect to said relatively uniform mass surface.
The most preferred embodiment of the present method has the transmitting and receiving antennae angled about 30 degrees with respect to the relatively uniform mass surface.